Web conveying apparatus with brake

ABSTRACT

A conveying apparatus includes: a conveyor including a brake to apply brakes to a web, the conveyor configured to convey the web while giving tension to the web by applying brakes to the web using torque of the brake; and a controller configured to control the conveyor. The controller performs at least one of a first control or a second control. The first control includes determining a first torque of the brake during acceleration of the web to be a value depending on a first inertial load at the conveyor during the acceleration of the web. The second control includes determining a second torque of the brake during deceleration of the web to be a value depending on a second inertial load at the conveyor during the deceleration of the web.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2017-190216, filed on Sep. 29, 2017, the entire contents of which are incorporated herein by reference.

BACKGROUND 1. Technical Field

The disclosure relates to a conveying apparatus for conveying a web.

2. Related Art

Japanese Patent No. 4164654 describes a printing apparatus that conveys a long-length web as a print medium while printing images on the web.

In the above printing apparatus, to obtain favorable print image quality, a tension generating mechanism gives tension to the web and keeps the tension of the web constant during printing.

SUMMARY

At the start of conveyance of a web, the above printing apparatus accelerates the web and stops the acceleration when the conveyance speed reaches the speed for printing. At that time, the tension of the web changes due to sudden absence of the acceleration, which sometimes causes slack in the web. Meanwhile, at deceleration from the conveyance speed for printing at the end of the conveyance of the web, the deceleration changes the tension of the web, which sometimes causes slack in the web.

In printing apparatuses that perform printing on a web using inkjet heads, when slack occurs in the web due to a tension change of the web as described above, the web comes into contact with the inkjet head and damages it in some cases. To address this issue, there is an idea of keeping constant the tension of the web during conveyance, including during acceleration and deceleration of the web in which printing is not performed.

If the acceleration level during acceleration and deceleration of the web is reduced, the tension change of the web as described above is also reduced. However, in this case, it will take a longer time to accelerate or decelerate the web, increasing waste portions of the web that are not used for printing.

The disclosure is directed to a conveying apparatus capable of reducing tension changes of the web while suppressing the increase of waste portions of the web.

A conveying apparatus in accordance with some embodiments includes: a conveyor including a brake to apply brakes to a web, the conveyor configured to convey the web while giving tension to the web by applying brakes to the web using torque of the brake; and a controller configured to control the conveyor. The controller is configured to perform at least one of a first control or a second control. The first control includes determining a first torque of the brake during acceleration of the web to be a value depending on a first inertial load at the conveyor during the acceleration of the web. The second control includes determining a second torque of the brake during deceleration of the web to be a value depending on a second inertial load at the conveyor during the deceleration of the web.

The configuration above is capable of reducing tension changes of the web while suppressing the increase of waste portions of the web.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram of a printing apparatus according to a first embodiment.

FIG. 2 is a control block diagram of the printing apparatus illustrated in FIG. 1.

FIG. 3A is a diagram illustrating transition of the conveyance speed of the web.

FIG. 3B is a diagram illustrating transition of an inertial load during conveyance of the web.

FIG. 4A is a diagram illustrating transition of the torque of a brake in the first embodiment.

FIG. 4B is a diagram illustrating a waveform of a control signal for the brake in the first embodiment.

FIG. 5 is a flowchart for explaining operation of a conveyor.

FIG. 6A is a diagram illustrating transition of the torque of a brake in a second embodiment.

FIG. 6B is a diagram illustrating a waveform of a control signal for the brake in the second embodiment.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

Description will be hereinbelow provided for embodiments of the present invention by referring to the drawings. It should be noted that the same or similar parts and components throughout the drawings will be denoted by the same or similar reference signs, and that descriptions for such parts and components will be omitted or simplified. In addition, it should be noted that the drawings are schematic and therefore different from the actual ones.

FIG. 1 is a schematic configuration diagram illustrating a printing apparatus 1 including a conveying apparatus according to a first embodiment of the disclosure. FIG. 2 is a control block diagram of the printing apparatus 1 illustrated in FIG. 1. Note that the upward, downward, right, and left directions in the following description are the same as those on the paper surface of FIG. 1. In addition, the direction orthogonal to the paper surface of FIG. 1 is defined as the front-rear direction. In FIG. 1, the right direction, left direction, upward direction, and downward direction are indicated by RT, LT, UP, and DN, respectively.

As illustrated in FIGS. 1 and 2, the printing apparatus 1 according to the first embodiment includes an unwinder 2, a conveyor 3, printers 4A and 4B, a rewinder 5, and a controller 6. The conveyor 3 and the controller 6 are included in the conveying apparatus.

The unwinder 2 unwinds a web W from a web roll 7 and conveys it to the conveyor 3. The web roll 7 is a web W, which is a long-length print medium, such as paper or film, rolled in a roll shape. The unwinder 2 includes a web-roll supporting shaft 11, a pair of delivery rollers 12, buffers 13 and 14, an unwinding motor 15, a delivery motor 16, motor drivers 17 and 18, and speed reducers 19 and 20.

The web-roll supporting shaft 11 rotatably supports the web roll 7.

The pair of delivery rollers 12 nips the web W unwound from the web roll 7 and conveys it toward the conveyor 3. One delivery roller 12 of the pair of delivery rollers 12 is rotationally driven by the delivery motor 16, and the other delivery roller 12 is rotated by the one delivery roller 12. The pair of delivery rollers 12 is disposed on the right side of the web-roll supporting shaft 11.

The buffer 13 holds slack of the web W between the web-roll supporting shaft 11 and the delivery rollers 12. The buffer 13 includes support rollers 21 and 22 and a dancer roller 23.

The support rollers 21 and 22 support the web W between the web roll 7 and the delivery rollers 12. The support rollers 21 and 22 are apart from each other in the right-left direction and disposed at the same height.

The dancer roller 23 pushes down the web W between the support rollers 21 and 22 by its own weight. With this operation, the slack of the web W between the web roll 7 and the delivery rollers 12 is absorbed by the buffer 13. The dancer roller 23 moves up and down by fluctuation of the slack amount of the web W between the web-roll supporting shaft 11 and the delivery rollers 12.

The buffer 14 holds slack of the web W between the delivery rollers 12 and a guide roller 31 of the conveyor 3 described later. The buffer 14 includes support rollers 24 and 25 and an uplift suppressor 26.

The support rollers 24 and 25 support the web W while holding the slack of the web W between the delivery rollers 12 and the guide roller 31. The support rollers 24 and 25 are apart from each other in the right-left direction and disposed at the same height.

The uplift suppressor 26 suppresses uplift of the web W between the support rollers 24 and 25 caused by changes of the behavior of the web W.

The unwinding motor 15 rotates the web-roll supporting shaft 11. The unwinding motor 15 rotates the web-roll supporting shaft 11 in the clockwise direction in FIG. 1, so that the web roll 7 rotates in the same direction, and the web W is unwound downstream (rightward).

The delivery motor 16 rotationally drives one delivery roller 12 of the pair of delivery rollers 12.

The motor drivers 17 and 18 drive the unwinding motor 15 and the delivery motor 16, respectively.

The speed reducer 19 transmits the rotation of the output shaft of the unwinding motor 15 to the web-roll supporting shaft 11 at a specified speed reduction ratio. The speed reducer 20 transmits the rotation of the output shaft of the delivery motor 16 to the one delivery roller 12 at a specified speed reduction ratio.

The conveyor 3 conveys the web W unwound from the web roll 7 by the unwinder 2. The conveyor 3 includes guide rollers 31 to 40, twenty under-head rollers 41, a meandering controller 42, a pair of brake rollers 43, a brake 44, a brake driver 45, a pair of conveying rollers 46, a conveying motor 47, a motor driver 48, speed reducers 49 and 50, and an encoder 51.

The guide rollers 31 and 32 guide the web W between the unwinder 2 and the meandering controller 42. The guide roller 31 is disposed at a left end of the lower portion of the conveyor 3. The guide roller 32 is disposed between the guide roller 31 and a meandering control roller 56 of the meandering controller 42 described later. The guide rollers 31 and 32 are rotated by the web W being conveyed.

The guide rollers 33 to 39 guide the web W between the meandering controller 42 and the conveying rollers 46. The guide roller 33 is disposed slightly above the left side of a meandering control roller 57 of the meandering controller 42 described later. The guide roller 34 is disposed above the guide roller 33. The guide roller 35 is disposed at the same height as the guide roller 34 and on the right side of the guide roller 34. The guide roller 36 is disposed at a position below the guide roller 35 and higher than the guide roller 33. The guide roller 37 is disposed at a position on the left side of the guide roller 36, near the right side of the web W between the guide rollers 33 and 34, and at almost the same height as the guide roller 36. The guide roller 38 is disposed on the lower right side of the guide roller 37. The guide roller 39 is disposed below the guide roller 38 and slightly on the right side of the guide roller 38. The guide rollers 33 to 39 are rotated by the web W being conveyed.

The guide roller 40 guides the web W between the conveying rollers 46 and the rewinder 5. The guide roller 40 is disposed at a right end of the lower portion of the conveyor 3. The guide roller 40 is rotated by the web W being conveyed.

The under-head rollers 41 support the web W under head units 58 described later, between the guide rollers 34 and 35 and between the guide rollers 36 and 37. Ten under-head rollers 41 are disposed between the guide rollers 34 and 35; and ten, between the guide rollers 36 and 37. Two under-head rollers 41 are disposed immediately under each head unit 58. The under-head rollers 41 are rotated by the web W being conveyed.

The meandering controller 42 corrects meandering of the web W, which is fluctuation of the position in the width direction (front-rear direction) of the web W. The meandering controller 42 includes the meandering control rollers 56 and 57.

The meandering control rollers 56 and 57 are rollers for correcting the meandering of the web W while guiding the web W. The meandering control rollers 56 and 57 are rotated by the web W being conveyed. The meandering control rollers 56 and 57 are turned, by an unillustrated motor, and inclined relative to the width direction of the web W as viewed from the right-left direction to move the web W in the width direction to correct the meandering. The meandering control roller 56 is disposed on the right side of the guide roller 32. The meandering control roller 57 is disposed above the meandering control roller 56.

The pair of brake rollers 43 nips the web W and applies brakes to the web W being conveyed, using the brake force of the brake 44. The brake rollers 43 are disposed between the guide rollers 31 and 32. The brake rollers 43 are rotated by the web W being conveyed.

The brake 44 applies brakes to the web W via the brake rollers 43 to give tension to the web W between the conveying rollers 46 and the brake rollers 43. The brake 44 is constituted of a powder brake.

The brake driver 45 drives the brake 44.

The pair of conveying rollers 46 nips the web W and conveys the web W toward the rewinder 5. One conveying roller 46 of the pair of conveying rollers 46 is rotationally driven by the conveying motor 47, and the other conveying roller 46 is rotated by the one conveying roller 46. The pair of conveying rollers 46 is disposed between the guide rollers 39 and 40.

The conveying motor 47 rotationally drives the one conveying roller 46 of the pair of conveying rollers 46.

The motor driver 48 drives the conveying motor 47.

The speed reducer 49 transmits the rotation of one brake roller 43 of the pair of brake rollers 43 to the output shaft of the brake 44 at a specified speed reduction ratio. The speed reducer 50 transmits the rotation of the output shaft of the conveying motor 47 to the one conveying roller 46 at a specified speed reduction ratio.

The encoder 51 outputs a pulse signal at every specified rotation angle of the output shaft of the conveying motor 47.

The printers 4A and 4B print images on the front surface and the back surface of the web W, respectively. The printer 4A is disposed above and near the web W between the guide rollers 34 and 35. The printer 4B is disposed above and near the web W between the guide rollers 36 and 37. The printers 4A and 4B each include five head units 58.

The head unit 58, having an inkjet head (not illustrated), prints images by ejecting ink to the web W through the nozzle of the inkjet head. In each of the printers 4A and 4B, the five head units 58 eject inks of different colors.

The rewinder 5 rewinds the web W subjected to printing by the printers 4A and 4B. The rewinder 5 includes a buffer 61, a brake roller 62, a brake 63, a brake driver 64, a rewinding shaft 65, a rewinding motor 66, a motor driver 67, and speed reducers 68 and 69.

The buffer 61 holds slack of the web W between the guide roller 40 of the conveyor 3 and the brake roller 62. The buffer 61 includes support rollers 71 and 72, and a dancer roller 73.

The support rollers 71 and 72 support the web W between the guide roller 40 and the brake roller 62. The support rollers 71 and 72 are apart from each other in the right-left direction and deposed at the same height.

The dancer roller 73 pushes down the web W between the support rollers 71 and 72 by its own weight. With this operation, the slack of the web W between the guide roller 40 and the brake roller 62 is absorbed by the buffer 61. The dancer roller 73 moves up and down by fluctuation of the slack amount of the web W between the guide roller 40 and the brake roller 62.

The brake roller 62 applies brakes to the web W being wound by the rewinding shaft 65. The brake roller 62 is rotated by the web W being wound by the rewinding shaft 65.

The brake 63 applies brakes to the web W via the brake roller 62 to give tension to the web W being wound by the rewinding shaft 65. This operation prevents wrinkles or the like from occurring in the web W being wound by the rewinding shaft 65.

The brake driver 64 drives the brake 63.

The rewinding shaft 65 winds the web W and holds it.

The rewinding motor 66 rotates the rewinding shaft 65 in the clockwise direction in FIG. 1. The rotation of the rewinding shaft 65 winds the web W on the rewinding shaft 65.

The motor driver 67 drives the rewinding motor 66.

The speed reducer 68 transmits the rotation of the brake roller 62 to the output shaft of the brake 63 at a specified speed reduction ratio. The speed reducer 69 transmits the rotation of the output shaft of the rewinding motor 66 to the rewinding shaft 65 at a specified speed reduction ratio.

The controller 6 controls operation of each section of the printing apparatus 1. The controller 6 is constituted of a programmable logic controller (PLC) or the like and includes a CPU and a memory.

The controller 6, in printing, drives the unwinder 2, conveyor 3, and rewinder 5 to convey the web W and makes the head units 58 of the printers 4A and 4B eject ink to print images on the web W. At this time, the controller 6 performs control to convey the web W with the conveying roller 46 while giving tension to the web W using the torque of the brake 44 at the conveyor 3.

In addition, during acceleration at the start of conveyance of the web W and during deceleration at the end of conveyance of the web W, the controller 6 performs control to set the torque of the brake 44 to a torque in which the inertial load at the conveyor 3 during the acceleration and deceleration of the web W is taken into account, respectively.

Next, operation of the printing apparatus 1 will be described.

In printing with the printing apparatus 1, when a print job is inputted, the controller 6 controls the unwinder 2, conveyor 3, and rewinder 5 to start conveying the web W.

After starting conveying the web W, after the conveyance speed of the web W at the conveyor 3 reaches a specified print conveyance speed Um, the controller 6 performs control to make the printers 4A and 4B print images on the web W while making the conveyor 3 keep the conveyance speed of the web W at the print conveyance speed Um.

When printing images by the printers 4A and 4B based on the print job is finished, the controller 6 controls the unwinder 2, conveyor 3, and rewinder 5 to finish conveying the web W. With this process, the print operation finishes.

Next, description will be provided in detail for operation of the conveyor 3 during conveyance of the web W in printing operation as described above.

The controller 6 performs control to convey the web W with the conveying rollers 46 while giving tension to the web W at the conveyor 3 using the torque of the brake 44.

The controller 6 outputs a voltage Vi to the brake driver 45 to control the brake 44. The brake driver 45 converts the voltage Vi to a current I using the following formula (1) and outputs the current I to the brake 44.

I=Vi/Re  (1)

Here, Re is a resistance value of a circuit included in the brake driver 45 that converts the voltage into the current.

When the current I is supplied to the brake 44, the brake 44 generates a torque τb in accordance with the current I. The relationship between the current I and the torque τb at the brake 44 is expressed by the following formula (2).

τb=a×I ³ +b×I ² +c×I+d  (2)

Here, a, b, c, and d are coefficients that are determined by the characteristics of the brake 44, which is a powder brake.

The controller 6 drives and controls the conveying motor 47 via the motor driver 48 based on the conveyance speed of the web W calculated from the output pulse signal of the encoder 51 to control the conveyance speed of the web W driven by the conveying rollers 46.

The conveyance speed of the web W at the conveyor 3 is controlled as illustrated in FIG. 3A. FIG. 3B is a diagram illustrating transition of the inertial load during conveyance of the web W when the conveyance speed is controlled as illustrated in FIG. 3A. FIG. 4A is a diagram illustrating transition of the torque of the brake 44 during conveyance of the web W at the conveyor 3. FIG. 4B is a diagram illustrating the waveform of the control signal for the brake 44 to control the torque as illustrated in FIG. 4A. FIG. 5 is a flowchart for explaining operation of the conveyor 3.

Before starting conveying the web W, the controller 6 is outputting a voltage Vi0 to the brake driver 45 as the control signal of the brake 44 as illustrated in FIG. 4B. With this operation, a torque τb0 is being generated at the brake 44 as illustrated in FIG. 4A. Here, Vi0 is an initial value of the voltage Vi outputted by the controller 6 to the brake driver 45 and is the output voltage for the brake driver 45 at the end of conveying the web W in the previous print operation.

When a print job is inputted, the controller 6 starts driving the conveying rollers 46 to start conveying the web W at step S1 in FIG. 5. After starting conveying the web W, the controller 6 increases the conveyance speed of the web W driven by the conveying roller 46 at a specified acceleration from time t1, the conveyance start time, as illustrated in FIG. 3A. The acceleration magnitude during this acceleration is set to the value at which the conveyance speed of the web W reaches the print conveyance speed Um a specified acceleration time N1 after the conveyance start.

In addition, at step S1 in FIG. 5, when the controller 6 starts conveying the web W, the controller 6 also sets the torque of the brake 44 to an acceleration torque τb1 as illustrated in FIG. 4A. Specifically, as illustrated in FIG. 4B, the controller 6 switches the output voltage for the brake driver 45 from Vi0 to Vi1 at time t1. Vi1 is a voltage to cause the brake 44 to generate the acceleration torque τb1. The acceleration torque τb1 is a torque in which the inertial load Ta1 during acceleration of the web W illustrated in FIG. 3B is taken into account. The acceleration torque τb1 and the inertial load Ta1 will be described later in detail.

After the conveying rollers 46 start conveying the web W, the controller 6 determines at step S2 in FIG. 5 whether the conveyance speed of the web W has reached the print conveyance speed Um. If the controller 6 determines that the conveyance speed of the web W has not reached the print conveyance speed Um (NO at step S2), the controller 6 repeats step S2.

If the controller 6 determines that the conveyance speed of the web W has reached the print conveyance speed Um (YES at step S2), the controller 6, at step S3, makes the conveying roller 46 start constant-speed conveyance at the print conveyance speed Um from time t2, which is the time when the conveyance speed of the web W reaches the print conveyance speed Um, as illustrated in FIG. 3A.

In addition, at step S3 in FIG. 5, when the controller 6 starts the constant-speed conveyance at the print conveyance speed Um, the controller 6 also sets the torque of the brake 44 to a constant-speed conveyance torque τb2 as illustrated in FIG. 4A. Specifically, as illustrated in FIG. 4B, the controller 6 switches the output voltage for the brake driver 45 from Vi1 to Vi2 at time t2. Vi2 is a voltage to cause the brake 44 to generate the constant-speed conveyance torque τb2. The constant-speed conveyance torque τb2 will be described in detail later.

Next, at step S4 in FIG. 5, the controller 6 determines whether printing based on the print job by the printers 4A and 4B has finished. If the controller 6 determines that the printing has not finished (NO at step S4), the controller 6 repeats step S4.

If the controller 6 determines that the printing has finished (YES at step S4); at step S5, the controller 6 starts deceleration of the conveyance speed of the web W from the print conveyance speed Um driven by the conveying roller 46. Here, as illustrated in FIG. 3A, the controller 6 decelerates the conveyance speed of the web W driven by the conveying roller 46 at a specified acceleration (acceleration to reduce speed) from time t3, which is the time when the deceleration starts. The acceleration to reduce speed during this deceleration is set to a value at which the conveyance speed of the web W reaches zero a specified deceleration time N2 after the deceleration from the print conveyance speed Um starts. Note that the deceleration time N2 may be the same as or may be different from the acceleration time N1.

In addition, at step S5 in FIG. 5, when the controller 6 starts reducing the conveyance speed of the web W, the controller 6 also sets the torque of the brake 44 to a deceleration torque τb3 as illustrated in FIG. 4A. Specifically, as illustrated in FIG. 4B, the controller 6 switches the output voltage for the brake driver 45 from Vi2 to Vi3 at time t3. Vi3 is a voltage to cause the brake 44 to generate the deceleration torque τb3. The torque τb3 is a torque in which the inertial load Ta2 during deceleration of the web W illustrated in FIG. 3B is taken into account. The deceleration torque τb3 and the inertial load Ta2 will be described in detail later.

Note that in the example illustrated in FIGS. 4A and 4B, Vi0 and Vi3 are the same value, and τb0 and τb3 are the same value.

After the reduction of the conveyance speed of the web W starts, as illustrated in FIG. 3A, the conveyance speed of the web W becomes zero at time t4, which is deceleration time N2 after the deceleration start time t3. With this operation, at step S6 in FIG. 5, the conveyance of the web W finishes and the series of operations finishes.

Next, the constant-speed conveyance torque τb2 will be described. The constant-speed conveyance torque τb2 is a torque of the brake 44 to give the web W a specified set tension Tp during the constant-speed conveyance of the web W.

The relationship between the constant-speed conveyance torque τb2 and the set tension Tp is expressed by the following formula (4).

Tp=τb2×G/rb  (4)

Here, rb is the radius of the brake roller 43 to which the brake 44 is connected. G is the speed reduction ratio of the speed reducer 49 connected to the brake 44.

Assuming that I2 is a current to cause the brake 44 to generate the constant-speed conveyance torque τb2, substituting τb2 for τb and substituting I2 for I in the foregoing formula (2) yields the following formula (5).

τb2=a×I2³ +b×I2² +c×I2+d  (5)

I2 is expressed by the following formula (6) yielded by substituting I2 for I and substituting Vi2 for Vi in the forgoing formula (1).

I2=Vi2/Re  (6)

Obtained from formulae (4) to (6) is the following formula (7).

Tp=Ka×Vi2³ +Kb×Vi2² +Kc×Vi2+Kd  (7)

Here, Ka to Kd are respectively expressed by the following formulae (8) to (11).

Ka=a×G/(rb×Re ³)  (8)

Kb=b×G/(rb×Re ²)  (9)

Kc=c×G/(rb×Re)  (10)

Kd=d×G/rb  (11)

The voltage Vi2 to cause the brake 44 to generate the constant-speed conveyance torque τb2 is obtained by solving formula (7) for Vi2.

Next, description will be provided for the inertial load Ta1 during the acceleration of the web W and the acceleration torque τb1.

The inertial load Ta1 during the acceleration of the web W is the product of Ja, which is the total of the moments of inertia of all the rollers in the section between the brake rollers 43 and the conveying rollers 46, which is the section where a tension is generated at the conveyor 3, and al, which is the angular acceleration of the brake rollers 43 during the acceleration of the web W. In other words, the inertial load Ta1 during the acceleration of the web W is calculated by the following formula (12).

Ta1=Ja×α1  (12)

Here, Ja, the total of the moments of inertia of all the rollers in the section between the brake rollers 43 and the conveying rollers 46 in the conveyor 3, is the total of the moments of inertia of the guide rollers 31 to 40, the twenty under-head rollers 41, the pair of brake rollers 43, the pair of conveying rollers 46, and the meandering control rollers 56 and 57.

Assuming that r is the radius of a roller, L is the length, and M is the mass, the moment of inertia J of the roller is calculated using the following formula (13).

J=M×r ²/2  (13)

The moment of inertia J of each roller in the section between the brake rollers 43 and the conveying rollers 46, described above, is calculated using formula (13), and then Ja is calculated by summing these results.

The angular acceleration α1 of the brake rollers 43 during the acceleration of the web W is calculated using the following formula (14).

α1=Ur/N1  (14)

Here, Ur is the angular speed of the brake roller 43 during the constant-speed conveyance of the web W (time t2 to t3) and is expressed by the following formula (15).

Ur=Um/(rb×G)  (15)

The acceleration torque τb1 is to make the tension of the web W the set tension Tp also during acceleration of the web W. The acceleration torque τb1 is a torque obtained by subtracting the inertial load Ta1 during the acceleration of the web W from the constant-speed conveyance torque τb2. Specifically, the acceleration torque τb1 is expressed by the following formula (16).

τb1=τb2−Ta1  (16)

The torque τb1 for acceleration can by calculated using formulae (4), (12), and (16).

Assuming that I1 is a current to cause the brake 44 to generate the acceleration torque τb1, substituting τb1 for τb and substituting I1 for I in the foregoing formula (2) yields the following formula (17).

τb1=a×I1³ +b×I1² +c×I1+d  (17)

I1 is calculated by solving formula (17) for I1.

Then, the voltage Vi1, which is supplied to the brake driver 45 to set the torque of the brake 44 to the acceleration torque τb1, is obtained using the following formula (18).

Vi1=Re×I1  (18)

Next, description will be provided for the inertial load Ta2 during the deceleration of the web W and the deceleration torque τb3.

The inertial load Ta2 during the deceleration of the web W is the product of the foregoing Ja, which is the total of the moments of inertia of all the rollers in the section where a tension is generated, and α2, which is the angular acceleration of the brake rollers 43 during the deceleration of the web W. In other words, the inertial load Ta2 during the deceleration of the web W is calculated by the following formula (19).

Ta2=Ja×α2  (19)

The angular acceleration α2 of the brake rollers 43 during the deceleration of the web W is calculated using the following formula (20).

α2=−Ur/N2  (20)

The deceleration torque τb3 is to make the tension of the web W the set tension Tp also during the deceleration of the web W. The deceleration torque τb3 is a torque obtained by adding the magnitude of the inertial load Ta2 during the deceleration of the web W to the constant-speed conveyance torque τb2. Specifically, the deceleration torque τb3 is expressed by the following formula (21).

τb3=τb2+|Ta2|  (21)

The deceleration torque τb3 can be calculated using formulae (4), (19), and (21).

Assuming that 13 is a current to cause the brake 44 to generate the deceleration torque τb3, substituting τb3 for τb and substituting 13 for I in the foregoing formula (2) yields the following formula (22).

τb3=a×I3³ +b×I3² +c×I3+d  (22)

I3 is calculated by solving formula (22) for I3.

Then, the voltage Vi3, which is supplied to the brake driver 45 to set the torque of the brake 44 to the deceleration torque τb3, is obtained using the following formula (23).

Vi3=Re×I3  (23)

As described above, in the printing apparatus 1, the controller 6 performs control during acceleration and deceleration of the web W to set the torque of the brake 44 to a torque in which the inertial load at the conveyor 3 during the acceleration and deceleration of the web W is taken into account, respectively. This operation reduces the influence of the inertial load to the tension during acceleration and deceleration of the web W, which in turn reduces tension changes of the web W from the start of conveyance of the web W to the end of the conveyance.

Here, unlike this embodiment, in the case where the torque of the brake 44 is set to the same torque as in the constant-speed conveyance also during acceleration and deceleration of the web W without the inertial load taken into account, the influence of the inertial load makes the tension of the web W during acceleration larger than the set tension and the tension of the web W during deceleration smaller than the set tension. As a result, when the acceleration of the web W finishes, the tension decreases, and the web W slackens. This may cause the web W to come into contact with the inkjet head of the head unit 58. Also during deceleration of the web W, the reduction of the speed decreases the tension, causes the slack of the web W, and may cause the web W to come into contact with the inkjet head. In contrast, this embodiment reduces the tension changes of the web W from the start of conveyance of the web W to the end of the conveyance and reduces the chance of the web W coming into contact with the inkjet head, as described above.

Also, in the printing apparatus 1, controlling the torque of the brake 44 reduces the tension changes of the web W without decreasing the acceleration of the web during acceleration and deceleration, which suppresses the increase of waste portions of the web W that are not used for printing (waste paper).

Thus, the printing apparatus 1 is capable of reducing the tension changes of the web W while suppressing the increase of waste portions of the web W.

Next, description will be provided for a second embodiment configured by changing a part of the first embodiment.

The general configuration of a printing apparatus 1A according to the second embodiment is the same as that of the printing apparatus 1 according to the first embodiment illustrated in FIGS. 1 and 2.

The second embodiment is different from the first embodiment in that when the torque of the brake 44 is changed, the torque of the brake 44 is gradually changed.

FIG. 6A is a diagram illustrating transition of the torque of the brake 44 while the web W is being conveyed in the conveyor 3 in the second embodiment. FIG. 6B is a diagram illustrating the waveform of the control signal for the brake 44 to control the torque as illustrated in FIG. 6A.

As illustrated in FIG. 6A, when changing the torque of the brake 44 to set it to a torque in which the inertial load is taken into account and when changing the torque of the brake 44 at the time of finishing the torque setting in which the inertial load is taken into account, the controller 6 gradually changes the torque of the brake 44.

Specifically, when changing the torque of the brake 44 from the torque τb0, which is the torque before starting conveying the web W, to the acceleration torque τb1, the controller 6 starts decreasing gradually the output voltage for the brake driver 45 from Vi0 at time t1, which is the time when the conveyance of the web W starts, as illustrated in FIG. 6B. Then, after the output voltage reaches Vi1, the controller 6 keeps the voltage Vi1 until time t2, which is the time when the acceleration of the web W finishes. Through this operation, as illustrated in FIG. 6A, the torque of the brake 44 gradually changes from τb0; after the torque reaches τb1, the torque τb1 is kept until time t2.

In addition, when changing the torque of the brake 44 from the acceleration torque τb1 to the constant-speed conveyance torque τb2, the controller 6 gradually increases the output voltage for the brake driver 45 from Vi1 from time t2, which is the time when the acceleration of the web W finishes, as illustrated in FIG. 6B. Then, after the output voltage reaches Vi2, the controller 6 keeps the voltage Vi2 during constant-speed conveyance of the web W. With this operation, as illustrated in FIG. 6A, the torque of the brake 44 gradually changes from τb1; after the torque reaches τb2, the torque τb2 is kept until time t3.

In addition, when changing the torque of the brake 44 from the constant-speed conveyance torque τb2 to the deceleration torque τb3, the controller 6 gradually increases the output voltage for the brake driver 45 from Vi2 from time t3, which is the time when the deceleration of the web W starts, as illustrated in FIG. 6B. Then, after the output voltage reaches Vi3, the controller 6 keeps the voltage Vi3. With this operation, as illustrated in FIG. 6A, the torque of the brake 44 gradually changes from τb2; after the torque reaches τb3, the torque τb3 is kept.

The reason why the torque of the brake 44 is changed gradually as described above is to reduce the tension changes of the web W caused by sudden changes in the torque of the brake 44.

The rate of change when the torque of the brake 44 is gradually changed is determined based on experiments, for example, such that the magnitude of vibration caused by the tension change of the web W due to the torque change of the brake 44 is reduced within the range that does not allow the web W to come into contact with the inkjet head.

The rate of change when the torque of the brake 44 is gradually changed from the acceleration torque τb1 to the constant-speed conveyance torque τb2 is set such that the torque change of the brake 44 finishes by the print preparation completion timing set in advance in the printing apparatus 1A.

The reasons for these are as follows. Specifically, if the torque change of the brake 44 finishes after print preparation is completed and printing starts, irregularities of the behavior of the web W due to the tension change at the time when the torque change finishes may decrease print image quality. If the print start timing is delayed to avoid such deterioration in the print image quality, waste paper increases. With these taken into account, to avoid the increase of waste paper and also the deterioration in the print image quality, the rate of change when the torque is gradually changed from the acceleration torque τb1 to the constant-speed conveyance torque τb2 is set so that the torque change of the brake 44 can finish by the timing of the print preparation completion, as described above.

As has been described, when changing the torque of the brake 44 in the second embodiment, the controller 6 gradually changes the torque of the brake 44, which reduces the tension change of the web W due to a sudden change in the torque of the brake 44. Through this operation, it is possible to further reduce the tension change of the web W.

In the first and second embodiments, the control is performed to set, during acceleration and deceleration of the web W, the torque of the brake 44 to a torque in which each inertial load is taken into account. However, either one of the controls may be omitted—the control to set the torque of the brake 44 during acceleration of the web W to a torque in which the inertial load during acceleration of the web W is taken into account or the control to set the torque of the brake 44 during deceleration of the web W to a torque in which the inertial load during deceleration of the web W is taken into account. Also in this case, it is possible to make the tension of the web W during acceleration or deceleration equal to the set tension for constant-speed conveyance, and thus reduce the tension change of the web W.

In the first and second embodiments, description has been provided assuming that the brake 44 is constituted of a powder brake; however, the brake 44 may be a brake of another type.

An embodiment according to the disclosure, for example, includes the following configuration.

A conveying apparatus includes: a conveyor including a brake to apply brakes to a web, the conveyor configured to convey the web while giving tension to the web by applying brakes to the web using torque of the brake; and a controller configured to control the conveyor. The controller is configured to perform at least one of a first control or a second control. The first control includes determining a first torque of the brake during acceleration of the web to be a value depending on a first inertial load at the conveyor during the acceleration of the web. The second control includes determining a second torque of the brake during deceleration of the web to be a value depending on a second inertial load at the conveyor during the deceleration of the web.

Upon changing the torque of the brake to the first torque or the second torque and upon changing the torque of the brake from the first torque or the second torque to another torque, the controller may be configured to gradually change the torque of the brake.

The conveyor may include a brake roller configured to be rotated by the web unwound from a web roll, and the brake may be configured to apply brakes to the web via the brake roller.

The controller may be configured to determine the first torque to be a value obtained by subtracting the first inertial load from a third torque of the brake during constant-speed conveyance of the web.

The controller may be configured to determine the second torque to be a value obtained by adding the second inertial load to a third torque of the brake during constant-speed conveyance of the web.

The first inertial load may be a product of a total of moments of inertia of all rollers for conveying the web including the brake roller in a section where the tension is generated in the conveyor and an angular acceleration of the brake roller during the acceleration of the web.

The second inertial load may be a product of a total of moments of inertia of all rollers for conveying the web including the brake roller in a section where the tension is generated in the conveyor and an angular acceleration of the brake roller during the deceleration of the web.

Embodiments of the present invention have been described above. However, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Moreover, the effects described in the embodiments of the present invention are only a list of optimum effects achieved by the present invention. Hence, the effects of the present invention are not limited to those described in the embodiment of the present invention. 

What is claimed is:
 1. A conveying apparatus comprising: a conveyor including a brake to apply brakes to a web, the conveyor configured to convey the web while giving tension to the web by applying brakes to the web using torque of the brake; and a controller configured to control the conveyor, wherein the controller is configured to perform at least one of a first control or a second control, the first control including determining a first torque of the brake during acceleration of the web to be a value depending on a first inertial load at the conveyor during the acceleration of the web, the second control including determining a second torque of the brake during deceleration of the web to be a value depending on a second inertial load at the conveyor during the deceleration of the web.
 2. The conveying apparatus according to claim 1, wherein upon changing the torque of the brake to the first torque or the second torque and upon changing the torque of the brake from the first torque or the second torque to another torque, the controller is configured to gradually change the torque of the brake.
 3. The conveying apparatus according to claim 1, wherein the conveyor includes a brake roller configured to be rotated by the web unwound from a web roll, and the brake is configured to apply brakes to the web via the brake roller.
 4. The conveying apparatus according to claim 1, wherein the controller is configured to determine the first torque to be a value obtained by subtracting the first inertial load from a third torque of the brake during constant-speed conveyance of the web.
 5. The conveying apparatus according to claim 1, wherein the controller is configured to determine the second torque to be a value obtained by adding the second inertial load to a third torque of the brake during constant-speed conveyance of the web.
 6. The conveying apparatus according to claim 3, wherein the first inertial load is a product of a total of moments of inertia of all rollers for conveying the web including the brake roller in a section where the tension is generated in the conveyor and an angular acceleration of the brake roller during the acceleration of the web.
 7. The conveying apparatus according to claim 3, wherein the second inertial load is a product of a total of moments of inertia of all rollers for conveying the web including the brake roller in a section where the tension is generated in the conveyor and an angular acceleration of the brake roller during the deceleration of the web. 